Root-caused a "logo upload hangs, connection refused in browser
console" report: the qemu-vm module's defaults (1 core, 1024MB) are
too tight for this stack (MySQL + Redis + PHP-FPM + chromium for PDF
generation, each PDF request spawning a full multi-process browser
instance) under real concurrent load, and this VM boots with
panic_on_oom - so exhausting memory doesn't degrade gracefully, the
whole VM goes down and every connection starts refusing.
Reproduced directly: at the 1024MB default, even 2 concurrent PDF
generation requests triggered `redis-server invoked oom-killer` and a
kernel panic. Bumped to 2 cores / 2560MB, which comfortably survives
that same load (~1.4GB still free afterward) - verified via the exact
concurrent-request scenario that crashed the 1024MB config, not just
absence of errors.
virtualisation.cores/memorySize aren't options on a plain nixosSystem
in this nixpkgs (only nixosTest nodes get the qemu-vm module
automatically), so this also adds an explicit import of it.
Documented the underlying resource cost (chromium is a full browser
per PDF request, pm.max_children=8 means up to 8 can run concurrently)
in CLAUDE.md as an operational note for real deployments, not just
this test VM.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
awkawbandClaude Sonnet 5
b1fe86e9d5